Neurons and Glia (neuro)

Question 1

Reticular theory vs neuron doctrine

Answer 1

• the human brain is comprised of both neurones and glial cells - there are broad categories, comprising numerous cell types with different structures and functions

Question 2

Histological staining of neural tissue

Answer 2

• fixation - brain tissue is fixed for preservation and subsequently embedded (eg paraffin, frozen)
• sectioning - a microtome can cut slices from a block of embedded brain tissue

Question 3

Nissl stain and Golgi stain

Answer 3

• Nissl stain - comprised of a basic dye (eg cresyl violet) - stains the nuclei and Nissl bodies of neurons
• Golgi stain - comprised of a silver chromate solution - stains neurons and their projections

Question 4

Power of electron microscope

Answer 4

• neuron doctrine was supported by growing body of scientific evidence came with resolving power of electron microscope
• neurons are not continuous but are discrete individual units
  Light microscopy:
• has a limit of resolution of 0.1 uM
• space between neurons and approximately 0.02 uM (or 20nM)
  Electron microscopy:
• has a limit of resolution of 0.1 nM
• our insights into the fine structure of neurons have come from electron microscopy

Question 5

“Brainbow” mice

Answer 5

• fluorescence microscopy and genetic manipulation techniques (eg Cre-Lox) allows us to see brain regions and individual neurons/glial cells in breath-taking detail

Question 6

Neurons

Answer 6

• the information processing cells within the nervous system, highly specialised for the conduction and transmission of electrical and chemical signals
• a prototypical neuron consists of a cell body (soma), axon and dendrites

Question 7

Cell body (soma)

Answer 7

the cell body (soma) of a neuron contains the same organelles found in all human cells including:

• nucleus
• rough endoplasmic reticulum (RER)
• smooth endoplasmic reticulum (SER)
• Golgi apparatus
• mitochondrion

Question 8

Neuronal cytoskeleton

Answer 8

• is the internal ‘scaffolding’ that gives a neuron its characteristic shape
• comprised of microtubules, microfilaments and neurofilaments
• microtubules - a polymer of protein tubulin located in axons and dendrites and important in axoplasmic transport
• microfilaments - a polymer of protein actin found throughout the neuron but particularly abundant in axons and dendrites
• neurofilaments - type of intermediate filament particularly abundant in axons and important in regulating axonal shape
• promising biomarker for neurodegenerative disorders (eg Alzheimer’s)

Question 9

Axons

Answer 9

• highly specialised neuronal projections that conduct nerve impulses (or action potentials) within the nervous system comprised of various regions
  axons are comprised of:
• axon hillock - tapers away from the soma to form the initial segment of the axon
• axon ‘proper’ - axon can branch to form axon collaterals (and recurrent collaterals)
• axon terminal - site at which axon comes into contact with other neurons at a synapse
  glial cells are able to myelinate axons:
• myelin is a membranous sheath that wraps around and insulates axons
• gaps in myelin sheath are Nodes of Ranvier - highly enriched in voltage-gated Na+ ion channels

Question 10

Dendrites

Answer 10

• highly specialised neuronal projections that receive synaptic inputs from other neurons
• dendrites of a single neuron are collectively termed a ‘dendritic tree’
• dendrites of some neurons are covered with specialised structures termed ‘dendritic spines’ - small sacs of membrane that protrude from dendrites of some cells to receive synaptic input
• dendritic spine structure is sensitive to type and amount of synaptic activity
• number of conditions have been associated with abnormal dendritic spine number (eg Alzheimer’s, schizophrenia)

Question 11

Neurotransmission

Answer 11

• fundamental process that drives information transfer between neurons and their targets

Question 12

Classification of neurons: neuronal structure

Answer 12

• can be classified based on neuronal structure
• by total number of projections (or neurites)
• by their dendritic trees and dendritic spines
• by their connections - sensory, motor and interneurons
• by their axon length - golgi type l and golgi type ll

Question 13

Classification of neurons: gene expression

Answer 13

• can be classified based on gene expression
• by the neurotransmitter that they use - these differences arise due to differential expression of proteins involved in neurotransmitter synthesis, storage and release
• proteins: acetylcholine (ACh), GABA, glutamate, dopamine, serotonin, noradrenaline

Question 14

Glial cells

Answer 14

• support cells within nervous system and can be classified into 4 categories based on structure and function:
  1) astrocytes
  2) microglia
  3) ependymal cells
  4) oligodendrocytes/ Schwann cells

Question 15

Astrocytes

Answer 15

• star shaped glial cells that function to regulate, in a number of ways, the extracellular environment of brain
• most numerous type of glial cell within the human brain
• regulate the extracellular environment in brain by, for eg, enclosing synaptic junctions and actively removing neurotransmitters from synaptic cleft

Question 16

Microglia

Answer 16

• account for approx 5-15% of total CNS cell number depending on anatomical region
• broadly distributed in brain and spinal cord
  function in:
• phagocytosis of neuronal and glial debris (eg sites of injury)
• synaptic connection remodelling
• directing neuronal migration during brain development

Question 17

Ependymal cells

Answer 17

• type of glial cell that provide the lining of the ventricular system of both brain and spinal cord
• act as a physical barrier separating the brain tissue from cerebrospinal fluid (CSF)
• deficits in ependymal cell function have been linked with severe neurological condition hydrocephalus
  function in:
• osmotic regulation of cerebrospinal fluid
• flow of cerebrospinal fluid
• directing cell migration during brain development

Question 18

Oligodendrocytes and Schwann cells

Answer 18

• type of glial cells that function to provide myelin - a membranous sheath around axons - to neurons in nervous system
• differ in their location and in some other characteristics
• oligodendrocytes are situated in CNS
• Schwann cells are situated in PNS
• one oligodendrocyte contributes myelin to several axons whilst Schwann cells myelinate only a single axon